Sewing machine apparatus to prevent backlash of bobbin thread



Dec. 20, 1960 J. w. LAKIN 2,965,057

SEWING MACHINE APPARATUS TO PREVENT BACKLASH OF BOBBIN THREAD Filed Nov.24, 1958 7 I I I l p. I 5 I I I I 5 o llrlll'lnlllll (A 1; I I j -2| 3fig- 4 5 4 @WW JAMES Wigwa BY 5131 64 ws ifigw ATTORNEYS Unite StatesPatent F SEWING MACHINE APPARATUS TO PREVENT BACKLASH OF BOBBIN THREADJames W. Lakin, Mount Holly, N.C., assignor to American & Efiral Mills,Inc., Mount Holly, N.C., a corporation of North Carolina Filed Nov. 24,1958, Ser. No. 776,033

1 Claim. (Cl. 112-231) This invention relates to the prevention ofbacklash in sewing machines wherein lightweight plastic bobbins areused.

Metallic bobbins have long been used in sewing machines. The weight of ametallic bobbin is sufiiciently great to prevent any residual backlashof the metallic bobbin within its bobbin case whenever the operation ofthe sewing machine is stopped for any purpose. The use of a relativelylight plastic bobbin in a sewing machine as a substitute for themetallic bobbin has been contemplated because the plastic bobbin ischeaper to produce and may be made transparent for permitting the amountof thread remaining thereon to be readily visible at all times. Plasticbobbins having smooth exterior surfaces have been manufactured for usein sewing machines, but the use of such bobbins is not without itsattendant difliculties. The weight of a plastic bobbin is but a fractionof its metallic counterpart. Thus, upon ceasing the operation of asewing machine in which a plastic bobbin having smooth exterior surfacesis installed, there is a general tendency on the part of the relativelylight plastic bobbin to slip along the surface of the bobbin case inengagement with the plastic bobbin because of residual backlash from thesewing machine, resulting in entanglement of the bobbin thread andsubsequent jamming of the sewing machine.

To overcome this problem of residual backlash, the smooth surfacedplastic bobbin has required the assistance of a separate shim elementinterposed between it and the bobbin case for preventing slippage of thebobbin relative to the bobbin case upon stopping the sewing machine.While this arrangement has been satisfactory for its intended purpose,the use of the shim element has proved to be a nuisance because such anelement is not always readily available when needed for installation ofthe smooth surfaced plastic bobbin in the bobbin case of a sewingmachine and is frequently lost as well.

It is a primary object of this invention to provide in combination withthe bobbin case of a sewing machine, a relatively light plastic bobbinhaving a head thereon in engagement with a wall of the bobbin case, andmeans on the head of the bobbin to prevent slippage between the bobbinand the bobbin case when the sewing machine is stopped.

It is another object of this invention to provide in combination withthe bobbin case of a sewing machine, a relatively light plastic bobbinhaving a head thereon in engagement with a wall of the bobbin case, thehead of the bobbin being provided with a circular band of splines orprojections which serve to insure the frictional gripping of the bobbinwith the bobbin case, thereby preventing relative slippage therebetweenwhich could otherwise occur because of residual backlash from the sewingmachine when its operation is abruptly stopped.

It is another object of this invention to provide in combination withthe bobbin case of a sewing machine, a lightweight plastic bobbin havinga head thereon in engagement with a wall of the bobbin case. A circular2,965,057 Patented Dec. 20, 1930 band of spaced radially extending ribsor splines are integrally formed on the bobbin head for frictionalgripping of the bobbin case to prevent relative slippage therebetweenwhen the sewing machine is stopped. During the operation of the sewingmachine when relative rotation may occur between the plastic bobbin andthe bobbin case, the ribs act in the nature of fans or impellers tocirculate air through the spaces between adjacent ribs for coolingpurposes to counterbalance the additional heat which is created by theincreased frictional resistance, thus permitting frictional grippingbetween the bobbin and the bobbin case without developing a resultantheat of friction of increased magnitude.

Some of the objects of the invention having been stated, other objectswill appear as the description proceeds, when taken in connection withthe accompanying drawings, in which-- Figure 1 is a fragmentaryisometric view of a sewing machine, showing the bed slide plate moved toopen position to expose the bobbin case and the plastic bobbin disposedtherein;

Figure 2 is an enlarged vertical sectional view of the bobbin case withthe improved splined plastic bobbin disposed therein, taken along line2-2 in Figure 1;

Figure 3 is an enlarged vertical sectional view similar to that shown inFigure 2, but illustrating a smooth faced plastic bobbin disposed withinthe bobbin case and showing entanglement of the bobbin threads caused bythe slippage of the smooth faced plastic bobbin relative to the bobbincase because of residual backlash developed by the stopping of thesewing machine; and

Figure 4 is a greatly enlarged isometric view of the improved splinedplastic bobbin within the bobbin case, the bobbin case and the splinedbobbin being partially broken away for purposes of clarity.

Referring more specifically to the drawings, Figure 1 illustrates asewing machine designated generally by the reference numeral 10 with itsbed slide plate 11 moved to open position to expose a bobbin case orhousing 2% which receives a plastic bobbin 40.

The bobbin case 20 comprises a cylindrical shell 21 having a planarcircular bottom wall 22. The cylindrical shell 21 of the bobbin case 20includes a curved slot 23 extending from its upper edge to a medialpoint thereon and terminating in a delivery eye 24, as shown in Figure2.

An elongate leaf spring 30 is suitably attached at one end to theexterior surface of the cylindrical shell 21, the upper edge of the leafspring 30 being substantially flush with the upper edge of thecylindrical shell 21. The leaf spring 30 substantially overlies thecurved slot 23 formed in the cylindrical shell 21 of the bobbin case 20.

The relatively light plastic bobbin 40 relating to the present inventionis disposed within the bobbin case 20, as illustrated in Figures 2 and4. The bobbin 40 includes a cylindrical barrel or body portion 41 havinga longitudinal bore 42 therethrough and a circular disc-like head 43 ateach end thereof, the circular heads 43 being of enlarged diameterrelative to that of the barrel portion 41. Thread or yarn T is woundabout the barrel portion 41 of the bobbin 40 for feeding to the sewingmachine 10. The bobbin 40 is of unitary construction, being molded froma suitable transparent plastic material such as crystal polystyrene,modified polystyrenes, nylon, phenolic, cellulose acetate, modifiedcellulose acetate, methacrylate, polyethylene, ethyl cellulose, ureas ormelamines. Crystal polystyrene is a preferred plastic, however, becauseof its low cost and its low static characteristics. The lattercharacteristic is of great importance, since the formation of staticelectricity on the surfaces of a bobbin may result in serious problems,such as the tangling and breaking of the thread wound about the bobbin.

The outer surface on each circular head 43 of the bobbin 40 is providedwith means for insuring that the bobbin 40 will frictionally grip thebobbin case 20 and will not be subject to slippage with respect theretoupon the operation of the sewing machine being suddently stopped. Asshown most clearly in Figure 4, this means takes the form of a circularband of spaced radially eX- tending ribs, splines or projections 44, thecircular band of ribs 34, in each instance, being arrangedconcentrically with the bore 42 through the barrel portion 41. The inneredges of the ribs 44 are spaced radially outwardly of the bore 42through the barrel portion 41 to define therebetween a flat annularsurface and the outer edges of the ribs 44 are spaced radially inwardlyfrom the periphery of each circular head 43. Thus, a band of ribs 44projects outwardly from the outer surface of each circular head 43 toprovide frictional engagement between the plastic bobbin 40 and thebottom wall 22 of the bobbin case 20.

Since a circular band of ribs 44 is provided on the outer surface ofeach circular disc-like head 43% of the plastic bobbin 40, the bobbin 40may be disposed within the bobbin case with either of its circular heads43 in engagement with the bottom wall 22 of the bobbin case 20. Africtional gripping engagement is thereby assured between the plasticbobbin 40 and the bobbin case 20 to prevent the relatively light plasticbobbin 40 from slipping with respect to the bobbin case 20 because ofresidual backlash from the sewing machine 10 whenever its operation isstopped. Consequently, no problem of the bobbin thread T becomingentangled because of this residual backlash is encountered.

It will be observed in Figure 4 that the spaces between adjacent ribs 44comprising the circular band on the lower head 43 define a plurality ofradially extending passageways linking the central flat annular surfaceof the head 43 with its periphery. When the sewing machine 10 is inoperation, relative rotation may occur between the plastic bobbin 40 andthe bobbin case 20. In such an instance, the ribs 44 on the lower head43 act in the nature of fans or impellers for circulating air to aid incooling the engaging surfaces of the plastic bobbin 40 and the bobbincase 20, the air being circulated through the passageways defined by thespaces between adjacent ribs 44 to cool the entire outer surface on thelower head 43 of the plastic bobbin 40. Thus, any additional heat whichmay be created by the frictional gripping of the ribs 44 with the bottomWall 22 of the bobbin case 20 is counterbalanced by the cooling effectdescribed hereinabove.

Figure 3 illustrates a tangled condition of bobbin thread T wound on arelatively light plastic bobbin 40' having smooth planar outer surfaceson its circular disc-like heads 43' and disposed within a bobbin case20'. In this instance, the smooth outer surface of the circular head 43'in engagement with the bottom wall 22 of the bobbin case 20', affords nofrictional gripping engagement therewith. As a generalization, a smoothplastic surface has an inherent slippery characteristic. Thus, when thesewing machine 10 is stopped for any reason, the residual backlashtherefrom is frequently effective to rotate the plastic bobbin 40'within the bobbin case 20' because its relatively light weight is easilyovercome by such backlash action. As can be seen in Figure 3, theslippage of the plastic bobbin 40' relative to the bobbin case 20' en-'4 courages entanglement of the thread T wound about the bobbin 40'which jams the sewing machine 10 upon its subsequent operation,requiring the operator to stop the sewing machine 10 and clear theentangled thread condition before resuming work.

The cooperation between the circular band of ribs 44 provided on theouter surface of the downwardly disposed circular disc-like head 43 ofthe plastic bobbin 40 with the planar bottom wall 22 of the bobbin case20 obviates any such difficulties as described in the precedingparagraph. Thus, the use of relatively light plastic bobbins in sewingmachines may be accomplished in the absence of shim elements withoutcreating any backlash problem, which otherwise would result inentanglement of the bobbin thread. Since such a bobbin may be made froma transparent plastic material, the amount of thread remaining thereonis at all times readily visible through the upturned circular disc-likehead thereof enabling the operator to determine when the bobbin requiresrefilling. 7

There has been disclosed an improved relatively light plastic bobbinhaving ribs or splines provided on the outer surfaces of its circulardisc-like heads for frictional gripping engagement with the bottom wallof a bobbin case. Such an arrangement makes it practical to use atransparent plastic bobbin as a replacement for the heavier metallicbobbin without encountering a backlash problem.

In the drawings and specification, there has been set forth a preferredembodiment of the invention and, although specific terms are employed,they are used in a. generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being defined in theclaim.

I claim:

In a sewing machine having a bobbin case, the combination therewith of arelatively lightweight plastic bobbin received within said bobbin case,said bobbin comprising a cylindrical barrel portion and a pair ofdisc-like heads of enlarged diameter relative to said barrel portion onopposite ends of said barrel portion, each of said heads having an outersurface provided with a flat circular central portion and a circularband of radially extending ribs projecting outwardly from said outersurface in raised relationship with respect to said flat circularcentral portion, said circular band of ribs bounding the flat circularcentral portion of said head so as to be spaced radially outwardly withrespect to said cylindrical barrel portion, the circular band of ribs onone of said heads being in friction-gripping engagement with a Wall ofsaid bobbin case, the outer surface of said one head and said circularband of ribs thereon defining radially extending passageways betweenadjacent ribs in said circular band, the passageways communicating withthe flat circular central portion of said one head at their inner ends,and said ribs serving as impellers upon relative rotation occurringbetween said bobbin and said bobbin case to circulate air through thepassageways and over the outer surface of said one head for cooling saidouter surface, thereby offsetting the heat developed by the frictionalengagement between the circular band of ribs and the wall of the bobbincase.

References Cited in the file of this patent UNITED STATES PATENTS2,019,952 Chaflin Nov. 5, 1935 2,116,982 Rubel May 10, 1938 2,200,721Marinsky et al May 14, 1940 2,254,606 Gomez Sept. 2, 1941 UNITED STATESPATENT OFFICE CERTIFICATION OF CORRECTION Patent No 2,965,057 December20, 1960 James W, Lakin It is hereby certified that error appears in theabove numbered patent requiring correction and that the said LettersPatent should read as corrected below.

In the grant, lines 2 and 12, and in the heading to the printedspecification, lines 4 and 5, name of assignee, for "American 81 EfiralMills, Inca. read American 81 Efird Mills, Inc,

Signed and sealed this 30th day of May 1961,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

